Method and apparatus for compensating for fixed pattern noise in an imaging system

ABSTRACT

There is described a pixel value adjustment method and apparatus. In one embodiment, pixel values can be adjusted by execution of an algorithm for adjusting pixel values. In one embodiment, an apparatus capable of executing an algorithm for adjusting pixel values is capable of operating in a decoding operating application. In one embodiment, an apparatus capable of executing an algorithm for adjusting pixel values is capable of operating in a video display operating application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to image signal processing and inparticular to a method and apparatus for adjusting pixel values.

2. Background of the Prior Art

When pixel values, representative of pixel voltages are read from animage sensor pixel array, slight inconsistencies are observable betweenthe voltages of the various pixels even when the array is exposed to ascene of uniform radiance. The inconsistency in the pixel values readfrom the various pixels is commonly referred to as “noise” either of afixed pattern noise type or a random noise type.

Fixed pattern noise refers to inconsistencies in the responsiveness ofan image sensor output that results from sensor characteristics orproperties affecting pixels of the sensor in the same way each time datais captured from those pixels. Random, or stochastic noise refers toinconsistencies which vary each time data is captured from the pixels.

While random, or stochastic noise cannot be compensated, it is useful toadapt an imaging system in video signal generating or decodingapplications to automatically compensate pixel values that deviate frompatterns that might be expected based on the array's radiance pattern.

Various problems have been noted in prior art imaging systems configuredfor fixed pattern noise compensation, both in set up routine methods forconfiguring an imaging system for fixed pattern noise compensation, andin methods for compensating pixel values read from a pixel array.

In one known setup routine for configuring an imaging system tocompensate for fixed pattern noise, a pixel array is exposed to uniform“dark frame” by shielding the pixel array from light. The pixel valuesread from the array during exposure to the dark frame are then used todetermine pixel offset terms. This method can be employed to estimate anadditive component of fixed pattern noise, but cannot be used todetermine a multiplicative component of fixed pattern noise.Furthermore, the setup method involving exposure to a dark frame issusceptible to measurement clipping. If a change in incident radiancedoes not result in a change in pixel value, then clipping has occurred.

In a known analog hardware method for compensating voltages read from apixel array, hardware components are provided and selectively activatedto compensate pixel voltages shifted out of a pixel array. A majorproblem with this scheme is that values read from the array can becorrected only to a small number of discrete voltages, thereby limitingthe precision of the correction. Also, this scheme requires additionalhardware.

Failure to compensate adequately for fixed pattern noise has significantconsequences, for example, when an imaging system is employed in indiciadecoding applications. In such applications, it is common to define anarea of interest in a captured image before decoding algorithmscommence. Fixed pattern noise has been observed to cause a symbologydecoding apparatus to misplace edge positions, and to result inerroneous identification of edge positions. The likelihood of anerroneous edge position identification increases when a decodingapparatus is employed to captured symbols having higher densities.

SUMMARY OF THE INVENTION

There is described a pixel value adjustment method and apparatus. In oneembodiment, pixel values can be adjusted by execution of an algorithmfor adjusting pixel pixel values is capable of operating in a decodingoperating application. In one embodiment, an apparatus capable ofexecuting an algorithm for adjusting pixel values is capable ofoperating in a video display operating application.

The features discussed above and other features of the invention willbecome clear to persons skilled in the art from a reading of a DetailedDescription of the Preferred Embodiments combined with the referenceddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like numerals are used to indicate the sameelements throughout the views,

FIG. 1 is a block diagram of an image processing system in which thepresent invention may be implemented;

FIG. 2 is a simplified graphical representation of a digital output ofan image sensor exposed to a scene of uniform radiance corresponding toa single row of pixels;

FIG. 3 shows a pixel array and an associated lens attached thereto;

FIG. 4 shows an electrical diagram of an image sensor illustratingschematic representations of electrical components of the image sensorwhose variance in physical properties gives rise to variance in emittedsignal output between the several pixels;

FIG. 5 a is a flow diagram of a configuration method for configuring animaging system to compensate for an additive component of pixel-specificfixed pattern noise;

FIG. 5 b is a flow diagram of a configuration method for configuring animaging system to compensate for an additive and multiplicativecomponent of pixel-specific fixed pattern noise.

FIG. 6 is a flow diagram of a configuration method for configuring animage system to compensate for column-dominant fixed pattern noise;

FIG. 7 is a table for use in describing a column dominant noisecompensation configuration method which summarizes average column whitevalues for a group of columns.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

There is described a pixel value adjustment method and apparatus. In oneembodiment, pixel values can be adjusted by execution of an algorithmfor adjusting pixel values. In one embodiment, an apparatus capable ofexecuting an algorithm for adjusting pixel values is capable ofoperating in a decoding operating application. In one embodiment, anapparatus capable of executing an algorithm for adjusting pixel value iscapable of operating in a video display operating application.

The invention relates to a method and apparatus for configuring animaging system to compensate for fixed pattern noise, variations inpixel values captured from an image sensor that vary according to afixed pattern. In a method for configuring an imaging system forcompensating an additive term component of fixed pattern noise, a pixelarray is exposed to a scene of known radiance and an average white valueis determined for each pixel of an array. Each average white value iscompared to a predetermined reference value to determine a correctionvalue for each pixel. In a method for configuring an imaging system forcompensating both an additive and multiplicative component of fixedpattern noise, a pixel array is exposed to a first scene having a firstknown radiance, and frames of the scene are captured, and then the arrayis exposed to a second scene having a second known radiance and framesof the second scene are captured. After first and second average whitevalues are determined for each pixel additive and multiplicative termcorrection values for each pixel are then determined by solving for asystem of equations relating the first and second average white valuesand first and second scene radiances. Correction values can be utilizedto correct pixel values of a frame of image data, and a decodingalgorithm for attempting to decode a frame of image data including pixelvalues can be activated.

According to its major aspects and broadly stated the present inventionrelates to a method and apparatus for configuring an imaging system tocompensate image signals for the effects of fixed pattern noise, whichaffects image sensor element outputs in the same way each time data iscaptured from those elements. An imaging system according to theinvention can include a setup mode of operation for determiningparameters for use in compensating fixed pattern noise, and a run modeof operation wherein the parameters determined in a setup mode are usedto compensate pixel values or values captured from the pixel elements.

Fixed pattern noise can result from a variety of sources. For examplefixed pattern noise can result from inconsistencies in the physicalproperties of electrical components of the image sensor such asswitching components associated with each pixel, or in certain types ofimage sensors with column amplifiers associated with each column. Fixedpattern noise can also result from certain illumination apparatusconfigurations. If the illumination is characteristically nonuniform,but its characteristics are fixed each time data is captured, then fixedpattern noise results. Another common source of fixed pattern noise isan optical phenomena known as the cosine⁴ (cosine) effect which resultsin outer pixels of an array receiving lower intensity ligh rays thancenter pixels on exposure to a scene of uniform radiance.

Fixed pattern noise associated with a pixel can be expressedmathematically byP_(M)=MP_(REF)+A Eq. 1

where P_(M) is the observed or measured pixel value, P_(REF) is areference value normally selected to correspond to an actual irradianceof light received at a pixel, M is a multiplicative or gain term, and Ais an additive, or offset term influencing fixed pattern noise.Typically, M is a value near unit and A is a small fraction of P_(M),the measured pixel Value. For some sources of fixed pattern noise, suchas the cosine effect, the multiplicative term is dominant while forother sources of fixed pattern noise, such as amplifier offset fixedpattern noise, the additive term is dominant. Other sources of fixedpattern noise have both significant multiplicative and significantadditive terms contributing to fixed pattern noise.

In certain setup routines that can be implemented according to theinvention which are best used in the case where the additive term ofifxed pattern noise is expected to be dominant, the multiplicative termof fixed pattern noise may be considered to be unitary. When themultiplicative term is assumed t be unitary, Eq. 1 reduces toP_(M)=P_(REF)+A Eq. 2

In a setup routine that can be implemented for determining only anadditive term of fixed pattern noise, an image sensor is exposed to ascene of uniform radiance, and a predetermined number of frames of thescene are captured in the system's memory. The gray scale value, orwhite value associated with each pixel of the pixel array image sensoris then calculated and also stored into memory. As the number ofpredetermined frames increases the contribution of zero mean randomnoise to the average white value diminishes since, by definition, zeromeans random noise is as likely to result in an increase in a pixelvalue as it is to result in a decrease in pixel value. That is, positiveand negative random noise terms tend to cancel each other as the numberof frames increases.

The scene of uniform radiance to which a pixel array is exposed ispreferably a gray scale uniform radiance scene, that is, a scene whichdoes not result either in a maximun clipped or minimum clipped pixelvalue being read from the pixels in the pixel array. By providing auniform radiance scene yielding gray scale pixel values between thesetwo limits, the problem of measurement clipping is avoided.

Once an average white value is determined for each pixel, a referencevalue is subtracted from an average white value to determine acorrection value for each pixel. The reference value, substituted forP_(REF) in Eq. 2 may be a predetermined gray scale value or may bedetermined based on the value of all or some of the remaining averagewhite values. The reference value normally corresponds to the actuallight irradiance of light falling on the pixel. While this value cannotbe measured directly, it can be assumed for the purposes of determininga correction value, in one simplified embodiment, that each pixel in anarray that is exposed to a scene of uniform radiance has equalirradiance of light falling thereon, or that pixels in a predefinedregion of an array have the same levels of irradiance received thereon.This is used to calculate the correction values. Once determined, thecorrection value associated with each pixel is stored into memory. Whenthe imaging system is switched from a setup mode to a run mode ofoperation, the correction values are retrieved from memory and used tocorrect pixel values of captured frames. Because the correction valuesare determined before the imaging system is switched from a setup modeof operation to a run mode of operation, the correction values areindependent of any image represented in the captured frames captured bythe imaging system when in a run mode of operation.

In a setup method that can be implemented accord according to theinvention for determining both multiplicative term and additive termsinfluencing fixed pattern noise a pixel array is exposed to at least twoscenes having uniform but differing radiances. It can be seen withreference to Eq. 1 that if the relationship between the differingradiances of the first and second scenes is known, the multiplicativeterm, along with the additive term of fixed pattern noise can bedetermined.

In accordance with a method that can be implemented for determining bothmultiplicative and additive fixed pattern noise terms, a plurality offrames of a pixel array are captured when the array is exposed to ascene of a first radiance, and a plurality of additional frames arecaptured when an array is exposed to a scene having a second radiance.In order to determine the multiplicative and additive terms for a givenpixel, the average white value of the pixel following exposure to thefirst scene is substituted for P_(M) in equation 1 in the development ofa first equation, and the average white value of the pixel followingexposure to the second scene is substituted for P_(M) in the developmentof a second equation. P_(REF) for a given pixel in the first and secondequations will normally correspond to the expected actual irradiance ofthe pixel during exposure to the first and second scenes, respectively.Solving for the set of two equations having two unknowns using wellknown computational methods solves for both the multiplicative andadditive components of fixed pattern noise.

Further aspects of the invention relate to methods and apparatuses forcompensating pixel values read from a pixel array, once the additiveterm and/or multiplicative term correction values have been determined.As discussed in the background, prior art compensation schemes includehardware components which are selectively activated so that voltagesread from a pixel array are automatically corrected in accordance withpreviously determined correction terms.

In th present invention, gray scale correction values can be stored inpredetermined memory locations o the imaging system. Preferably, so thatprocessing time is minimized, the correction terms are read from memoryand used to correct pixel values in the case of decoding applicationsonly when stored pixel values are read from memory during execution of adecoding algorithm. An advantage of the compensation method of thepresent invention is that the method of the present invention allowscorrection values to be selected between a large number of discretevalues, without requiring the providing of costly and space consumingphysical elements as in the prior art design. The correction method ofthe present invention may be used in combination with a hardwareimplemented compensation scheme.

An imaging system 10 having an image sensor 12 and control processor 14in which the present invention may be incorporated is shown in FIG. 1.

Image sensor 12 includes, on a single substrate a two dimensional array16 of light sensitive picture elements, or pixels upon which an opticalsystem is arranged to focus an image of indicia and further includes atiming and control circuit 18 for electrically addressing pixels P viahorizontal and vertical address lines 20 and 22, thereby causingelectrical signals representing the image to be read out of array 16 viaoutput 24 thereof. After amplification by amplifier 26, and conversionby analog-to-digital converter 28 the latter signals are output fromimage sensor 12 as serial digital parallel image data signals on linesD0=D7 or as a digital serial image data signal on data lines D0-D1.

Digital image data is supplied from sensor 12 to processor 14 with theaid of a first signal known as a frame start pulse and a second signalknown as data valid pulse. Because the use of such signals is well knownto those skilled in the art, their use will not be described in detailherein.

Image sensor control processor 14 preferably comprises a microprocessor30 which may be of either the single chip or multi-chip types, and whichmay include on chip and/or off chip program and data (working) memories32 and 34, depending upon the complexity of the program used to controlimage sensor 12 and to process image data produced thereby.Microprocessor 30 may be of the type which is formed on a singleintegrated circuit chip and which includes an on-chip read onlyprogrammable program memory 32 and an on-chip read-write working memory34. Microprocessor 30 may also be of the type which includes foureight-bit (I/O) ports, 40 through 46, each bit of each port beingindependently controlled by the stored program. Because microprocessorsystems of this type, and their multi-chip equivalents are well known tothose skilled in the art, microprocessor 30 will not be described indetail herein.

With reference now to specific attributes of the present invention, FIG.2 is a simplified representation of the digital output of image sensor12 when pixel array 16 is exposed to a scene of uniform radiance. Forpurposes of simplifying the description of the invention, the digitaloutput of FIG. 2 illustrates only 20 representative column values of thepixel columns in a commercially available pixel array, which areavailable in many different dimensions including 160 rows by 160 columns(in a VVL 1070 image sensor available from VLSI Vision Limited), andwhich are expected to become available in increasing densities. Theabove referenced VVL 1070 image sensor is a monochrome image sensor.

In an ideal image sensor, output 50 might be expected to yield anidentical pixel value for each pixel in a row on exposure to a scene ofuniform radiance. From row output 50 it is seen that an actual imagesensor does not exhibit such behavior. Instead, pixel values vary frompixel to pixel in the row. The variation, or inconsistency in the pixelvalues generated by the pixels in an array on exposure of the sensor toa uniform radiance scene is referred collectively to as “noise.”

Fixed pattern noise refers to a variation among pixel values resultingfrom factors affecting pixel values in the same way and to the sameextent each time data is read from the pixels.

One source of fixed pattern noise results from differences in the sizeand other physical characteristics of miniature integrated circuitcomponents. With reference to the pixel array schematic diagram of FIG.4 each pixel location 72, 74 has associated therewith switching circuitcomponent (not shown) and a separate column amplifier 80 is associatedwith each column of array 16. The voltages exhibited by pixels of thearray will vary from one another on exposure to a uniform radiance sceneas a result in part of slight differences in the physical properties ofswitching circuit components and amplifiers 80, and other electricalcomponents which may be associated with array 16. Column amplifiers arethe dominant source of fixed pattern noise in several types of availableimage sensors. Differences in the physical characteristics of opticalcomponents, namely of pixels 72, 74 of pixel array 16 can also give riseto noise that varies according to a fixed pattern.

Fixed pattern noise can also result from certain illumination apparatusconfigurations. If the illumination is characteristically nonuniform,but its characteristics are fixed every time an image is captured, thenfixed pattern noise results. An illumination apparatus can result infixed pattern noise if, for example, the illumination apparatus includesa bank of illuminators which are not precisely matched, or if one ormore illuminators are swept over a target scene. By correcting theeffects of fixed pattern noise, a truer representation of a given sceneis produced by an imaging system.

Another source of fixed pattern noise is an optical phenomena known asthe cosine⁴, or cosine effect, which is described with reference to FIG.3. According to the cosine effect, the irradiance at a given pixel 64 isproportional to the cosine to the fourth power of the angle 66 definedbetween optical axis 67 and pixel 64 as seen by lens 68. Therefore outerpixels, eg. 69 tend to have lower irradiances associated therewith thancenter pixels 70. A detailed discussion of the cosine effect appears inModern Optical Engineering, Smith, Warren J. (McGraw-Hill, 1966), pp.132-133.

Referring again to the block diagram of FIG. 1 aspects of imaging systemenabling system 10 to compensate for fixed pattern noise will bedescribed in detail. According to the invention, imaging system 10 hastwo modes of operation: A first, set up mode for configuring the systemfor compensating fixed pattern noise; and a second, run mode foroperating the system in one of several possible operating applicationssuch as bar code and other decoding operating applications, videodisplay operating applications, and video record operating applications.On-board control processor 14 which is integral with imaging system 10is normally configured to execute the set up mode of operation. However,an external processor (not shown) may in the alternative be configuredto carry out the setup routine, and control processor may be of a typethat is dedicated for executing a run mode of operation. The setup modeof operation may be executed only once during the lifetime of imagingsystem 10 at the location of production before imaging system 10 isdistributed to an end user.

The setup routines according to the invention, and the run modeoperation methods of the invention utilize a mathematical expression forfixed pattern noise which is given byP _(M) =MP _(REF) +A  Eq. 1where P_(M) is the observed, or measured pixel value, P_(REF) is areference value normally selected to correspond to an actual irradianceof light received at a pixel, M is a gain, or multiplicative term, and Ais an additive, or offset term influencing fixed pattern noise. For somesources of fixed pattern noise, such as the cosine effect, themultiplicative term is dominant while for other sources of fixed patternnoise the additive noise term is dominant. Other sources of fixedpattern noise have both significant multiplicative and significantadditive terms contributing to fixed pattern noise. Note that Eq. 1represents a first order process. It will be recognized that higherorder processes are possible and can be corrected for.

In certain setup routines according to the invention, which are bestused in the case where the additive term of fixed pattern noise isexpected to be dominant, the multiplicative term of fixed pattern noisemay be considered to be unitary. When the multiplicative term is assumedto be unitary, Eq. 1 reduces toP _(M) =P _(REF) +A  Eq. 2

A configuration method for determining only an additive component offixed pattern noise is described with reference to the flow diagram ofFIG. 5 a. In this method, pixel array 16 at step 102 is exposed to ascene of uniform radiance, and a predetermined number of frames of thescene are captured and stored in working memory 34. The average grayscale value, or the average white value generated by each pixel of thepixel array image sensor is then calculated at step 104 and also storedinto memory. Of course, according to a well known programming techniqueit is not necessary to store every test frame into memory. In adedicated memory location the running sum of white values may be storedand the average white value for a given pixel may be computed bydividing the running sum by the number of test frames captured. As thenumber of predetermined frames increases the contribution of zero meanrandom noise to average white value diminishes since, by definition,zero mean random noise is as likely to result in an increase in a pixelvoltage as it is to result in a decrease in pixel voltage. That is,positive and negative random noise terms tend to cancel each other asthe number of frames increases. Therefore as the number of framesincreases the average white value for each pixel converges on a valuerepresenting the contribution to the pixel signal from effects remainingstable each time data is recorded from the pixel.

The scene of uniform radiance to which a pixel array is exposed ispreferably a scene which yields pixel values between maximum clippingand minimum clipping pixel values by providing a scene yielding onlygray scale pixel values between these two limits, thus the problem ofmeasurement clipping is avoided. The uniform radiance scene can beapplied to a pixel array by, for example, application of a constantsource of irradiance to a Lambertian target (which may be supplied by asheet of white paper) positioned forward of the pixel array, or byapplication of an appropriate source of illumination directly to thepixel array, such as a light bulb directing light through a sheet ofmilk glass toward the pixel array, or by a CRT monitor directed at thearray. While a scene of uniform radiance is preferred for the purposesof simplifying various mathematical calculations required by theinvention as described herein, it will be recognized that the setuproutines of the invention can be executed by applying nonuniform scenesto the pixel array as long as radiance characteristics of the appliednonuniform scenes are known and controlled.

Referring again to the flow diagram of FIG. 5 a it is seen that once anaverage white value is determined for each pixel, a reference value,substituted for P_(REF) in Eq. 2, is subtracted from the average whitevalue at step 106 to determine a correction value for each pixel. Thereference value may be a predetermined gray scale value or may bedetermined based on the value of all or some of the remaining averagewhite values. For example, a reference value for a given pixel ofinterest may be determined by averaging average white values of pixelssurrounding and possibly including the pixels of interest. Oncedetermined, the correction associated with each pixel is stored,typically by writing the correction values into program memory 32. Whenthe system is switched to a “run” mode of operation, the correctionvalues are retrieved from memory 32 and used to correct pixel values ofcaptured frames captured from a scene. Because the correction values aredetermined before the imaging system is switched from a setup mode ofoperation to a run mode of operation, the correction values areindependent of any image represented in the captured frames captured bythe imaging system when in a run mode of operation.

When system 10 is in a “run” mode of operation, individual pixels may becorrected by the correction values according to one of a number ofpossible techniques. For example, the correction value associated witheach pixel can be read from ROM 32 and added to the pixel signal valuesbefore the pixel values are initially stored in RAM 34 or transmitted tofurther signal processing circuitry. Equivalent correction methodscorrecting pixel values after digital to analog but before storagememory can be implemented in digital hardware such as FPGA or an ASIC.In accordance with one embodiment of the invention, correction valuescan be read from ROM 32 and added to pixel values previously stored inRAM 34 only when captured frames of images are retrieved from RAM 34during execution of decoding applications. It is common in embodimentsof the invention to employ a direct memory access device (not shown)controlled by microprocessor 30 to aid in the transfer of frames ofpixel array data from image sensor to RAM 34 or to further video monitorcircuit components, thereby enhancing the speed and performancecapabilities of microprocessor 30.

A compensation method equivalent to the image sensor specific embodimentdescribed herein can be adapted for implementation in a 2D laserscanning device employed to correct for additive and multiplicativesignal variations in the system response over the scanning field ofview. In this embodiment the laser would scan the entire field of viewand over one or more optical sensors would receive the returned opticalsignal. The series of signals created in this fashion would be read intomemory together with clocking information from the scanning device. Thisdata can be processed in a fashion analogous to the image array datadiscussed herein.

A setup method for determining both multiplicative and additive termscontributing to fixed pattern noise is described with reference to FIG.5 b. In a setup method according to the invention for determining bothmultiplicative term and additive terms influencing fixed pattern noise apixel array is exposed to at least two scenes having uniform butdiffering radiances. It is seen with reference to Eq. 1 that if a pixelarray is exposed to two scenes having differing but known radiances, andthe relationship between the two scenes is known then a set of twoequations having two unknowns is formed:P _(M1) =MP _(REF1) +A  Eq. 3P _(M2) =MP _(REF2) +A  Eq. 4where P_(REF1) is a reference value normally selected to correspond tothe actual light irradiance received at pixels of an array onapplication of a scene of a first radiance and P_(REF2) is a referencevalue corresponding to the actual light irradiance of light received atpixels of an array on application of a scene having a second radiance.P_(M1) is the observed or measured pixel value of a pixel resulting fromapplication of the first scene, and P_(M2) is the measured pixel valueof a pixel resulting from application of the second scene.

According to a specific method for determining a multiplicative terminfluencing fixed pattern noise, a plurality of frames corresponding toa pixel array exposed to a scene having a first known radiance may becaptured at step 108 to determine, at step 109 an average white valuecorresponding to application of the first scene (so as to determine anaverage pixel value wherein contribution of random noise is reduced toan insignificant level), and then a plurality of frames of a pixel arrayexposed to a uniform radiance scene having a second radiance may becaptured to determine at step 110 an average observed pixel value foreach pixel corresponding to application of the second scene.Substituting the first and second average observed pixel values forP_(M1) and P_(M2) in Eqs. 3 and 4 respectively, equations 3 and 4 aresolved using well known mathematical methods at step 112 to determinethe multiplicative term, M and offset term, A, affecting fixed patternnoise for each pixel in working memory 34.

The determined values for M and A associated with each pixel are stored,preferably in ROM 32 and later used to compensate captured pixel valuesusing Eq. 1 when the unit is switched to a “run” mode of operation.

While the values P_(REF), P_(REF1), and P_(REF2) in equations 1, 3, and4, corresponding to actual pixel irradiance cannot be measured directly,certain assumptions can be made regarding actual pixel irradiance in thesolving for the set of equations 3, 4, and 5 or derivations thereof. Forexample, if a pixel array is exposed to a scene of uniform radiance itcan be assumed, for the purposes of carrying out the calculations thateach pixel in the pixel array has the same actual pixel irradiance.Alternatively one might assume that all the pixels in a local region ofan array have the same actual value. The latter assumption allows forgradual change in illumination incident upon the pixel array such as thechange due to the cosine effect when the scene is imaged through a lens.

A specialized embodiment of the invention implemented to compensate fora specific source of fixed pattern noise is described with reference toFIG. 6. In one embodiment of the invention, imaging system 10 isconfigured to compensate for column-dominant fixed pattern noise havinga dominant effect observable on a column-by-column basis. In a commontype of image sensor, fixed pattern noise results in part from slightinconsistencies in the physical properties of amplifiers 80 associatedwith each pixel column. In such image sensors, every pixel in a givencolumn is affected by the column amplifier associated with the column inthe same way. When column amplifiers are the dominant source of fixedpattern noise, a simplified setup routine of the invention can be madeto determine column correction values, for use in correcting each pixelof a given column. In this case, correction terms are computed andstored on a column by column basis rather than a pixel by pixel basis,resulting in a significant savings in memory storage space.

In one type of image sensor architecture as shown in FIG. 4 a columnamplifier 80 associated with each pixel of a column array typicallycomprises a pair of integrated circuit field effect transistors. It isrecognized that the consistency achievable between each column'samplification is limited by the precision with which each amplifier isfabricated.

In step 120 pixel array 16 is exposed to a scene of uniform radiance,and a plurality of frames are captured. Because column amplifiers in thesensor array for which the method was adapted were found to have adominant additive term, but a relatively insignificant multiplicativeterm influencing fixed pattern noise, the setup routine provides forpixel array exposure to a single scene of known radiance. It will berecognized, however, that finding a column-specific multiplicative fixedpattern noise term would require exposure to a scene having a secondknown radiance, as described in the method discussed in connection withFIG. 5 b. Referring again to the method described in connection withFIG. 6, it is seen that instead of storing into memory 34 each pixelvalue for each frame as in the case of a pixel-by-pixel noisecompensation configuration method, a column white value for each columnis determined at step 122 and stored after each frame is captured,thereby conserving memory space and calculation time relative to thetime and memory space required for setting up an imaging system forcompensating for pixel-by-pixel fixed pattern noise. The column whitevalue associated with each column is preferably determined by findingthe highest gray scale value present in a column, after a predeterminednumber (for example, the highest 6.25%) of the column's highest grayscale values are discarded. Alternatively, a column's column white valuemay be determined, for example, by finding an average gray scale valueassociated with all pixels of a column, or by finding an adjustedaverage white value of all pixels of a column, after selected high, low,or anomalous pixel values are discarded. After a column white value isdetermined for each column of each frame, the resulting set of columnwhite values are averaged at step 124 to determine an average columnwhite value for each column.

A correction value for each column is then determined by subtracting areference value from each average column white value, in accordance withEq. 2 wherein column reference value is substituted for P_(REF). As inthe case of a pixel-by-pixel compensation configuration method, thereference value may be a predetermined reference value or may be a valuedetermined based on the value of some or all of the remaining columnwhite values.

Step 126 for selecting or determining a reference value is explained indetail with reference to FIG. 7 showing a graph of average column whitevalues, which is constructed by finding the column white value for eachcolumn of data in each frame captured, and then averaging the columnwhite values. A reference value could be selected to be an arbitraryconstant value in the range of average column white values. If areference value is selected to be an arbitrary constant value, asrepresented by reference 130 in FIG. 7 then the same arbitrary constantvalue is subtracted from average column white value for each column forwhich a column correction value is determined.

For decoding applications, the inventors discovered that the quality ofthe decoding is improved if the column reference value in certainapplications is selected to be other than a constant reference. Inparticular, the inventors discovered that the quality of decoding isimproved if column reference values are selected to change in accordancewith a certain pattern of light irradiance that is known to fall on apixel array of conventional design.

According to the cosine effect described herein, the intensity of lightrays striking a pixel array exposed to a uniform radiance scene tend toresult in greater light irradiances at the location of center pixelsthan at the location of outer pixels.

Technically speaking, the cosine effect is a factor contributing tofixed pattern noise, and may be compensated for by selecting a columnreference value of a constant value. In video record or displayapplications it may be desirable to compensate for the cosine effect forenhancement of the video image quality. However, the inventors foundthat for decoding applications, the quality of the decoding is enhancedif reference values are selected to correct for neighbor-to-neighborpixel noise but are not selected to correct for sources resulting ingradual changes in pixel values such as the cosine effect. Gradualchanges in pixel voltages do not seriously affect the quality ofdecoding operations. Decoding operations, however, are seriouslyaffected if abrupt changes in pixel values are observed in neighboringpixels of an array exposed to a uniform radiance scene. The presence ofabrupt changes in pixel values of neighboring pixels exposed to auniform scene can result in a misplacement of edge positions or in anerroneous edge position detection.

To the end that reference values are selected to correct forneighbor-to-neighbor pixel noises but are not selected to correct forsources resulting in gradual changes in pixel values, a differentreference value may be determined for every column correction valuedetermined. In one embodiment of the invention, reference values fordetermining column correction values are determined by taking intoaccount the average column white values associated with the columnlocations surrounding the column location for which a reference value iscurrently being calculated. With reference to FIG. 7 a reference valuefor determining a correction value for a given column is determined byaveraging the column white value of the column of interest, e.g. 134,and the average column white values of a predetermined number ofsurrounding columns, e.g. columns 136 and columns 140. In one example ofthe invention, a reference value for determining each column'scorrection value is determined by averaging the average column whitevalue, corresponding to the column of interest, 24 columns preceding thecolumn of interest and 24 columns forward of the column of interest.

The method described herein of utilizing column white values associatedwith columns surrounding and possibly including the column of interestto determine a reference value for the column of interest is especiallyuseful in developing a selection of column reference values thataccurately reflect the impact of gradual changes on pixel values readfrom array. It will be recognized that the method can also be used toaccurately select reference values so that the reference valuesaccurately represent the impact on pixel radiance owing to other sourcesof fixed pattern noise. The concept of utilizing measured pixel valuedata in determining reference values can also be applied on a pixelspecific basis. For example the white values of pixels surrounding andpossibly including a pixel of interest can be used in determining areference value for use in determining a correction value for a specificpixel in a setup routine for determining pixel correction values.Specifically, a reference value for each pixel can be determined basedon the average white values of pixels surrounding and including thepixel of interest.

Further aspects of the invention relate to methods and apparatuses forcompensating values read from a pixel array, once additive term and/ormultiplicative term correction values have been determined according tothe equationP_(CORRECTED)=P_(M)−A)/Mwhere P_(CORRECTED) is the corrected pixel value as calculated utilizingcorrection terms A and M. As discussed in the background, prior artcompensation schemes include hardware components which are selectivelyactivated so that values read from a pixel array are automaticallybiased in accordance with previously determined correction terms.

In the correction method of the present invention, the time requirementsfor carrying out pixel value corrections is minimized by a schemewherein correction values are retrieved from memory, normally ROM 32 andused to correct pixel values, only when stored pixel values areretrieved from RAM 34 during the execution of a decoding algorithm. Thismethod greatly reduces the number of correction operations that have tobe executed. In many decoding apparatuses such as the Welch Allyn IT4400bar code reader, a region of interest is defined in a captured framebefore decoding operations commence. Using the correction method of thepresent invention, the number of correction operations that have to becarried out is reduced, because such corrections need only be made forthose pixel locations within the region of interest.

Another advantage of the correction method of the present inventionallows for the selection of correction values between a large number ofdiscrete values without requiring the providing of costly and spaceconsuming physical elements as in the design known in the prior art. Ifthe correction value is selected to be an 8 bit binary value then thecorrection value can be selected between 256 discrete values. To furtherthe resolution achievable with the correction method of the invention,the number of bits characterizing the correction value may be increasedor else the binary correction value may be used in combination with ananalog hardware compensation scheme.

There is described (A) a method for configuring an imaging system in aset-up mode of operation so that said imaging system compensates imagesignals generated by said imaging system for fixed pattern noise, saidimaging system having an image sensor including a pixel array and beingin communication with a control processor, said method comprising thesteps of: exposing said pixel array to a scene having a known radiance,said pixel array comprising a plurality of pixels; capturing apredetermined number of image signal frames of said scene intopredetermined storage locations of said processor, said each framecomprising a plurality of white values, said each white valuecorresponding to one of said pixels; averaging white valuescorresponding to at least one of said pixels to determine an averagewhite value for said at least one pixel of said pixel array; comparingsaid average white value to a predetermined reference value for said atleast one pixel, and therefrom determining a correction value for saidat least one pixel of said array; and storing said correction value intoa storage location of said processor for retrieval by said processorwhen said processor image signals from said sensor in a run mode ofoperation, (B) the method wherein in said comparing step, saidpredetermined reference value for said at least one pixel is a constantvalue in the range of pixel white values for said array, (C) the methodwherein said comparing step includes the step of determining a referencevalue for said at least one pixel based on the average white value of atleast one neighboring pixel surrounding said at least one pixel, (D) themethod wherein said comparing step includes the step of determining areference value for said st least one pixel based on the average whitevalues of pixels surrounding and including said at least one pixel, and(E) the method wherein said exposing step includes the step of exposingsaid pixel array to a scene having a radiance such that a reading ofminimum clipped or maximum clipped pixel value from said array does notresult from such exposure.

There is described (A) a method for configuring an imaging system in aset up mode of operation so that in a run mode of operation said imagingsystem compensates image signals generated by said imaging system forfixed pattern noise, said imaging system having an image sensorincluding a pixel array and being in communication with a controlprocessor, said method comprising the steps of: exposing said pixelarray to a scene having a known radiance; capturing a predeterminednumber of image signal frames of said known radiance scene and finding acolumn white value for each column of said array when said each frame iscaptured; averaging said column white values to determine an averagecolumn white value for each column of said pixel array; comparing saideach average column white value to a predetermined reference value foreach column, and therefrom determining a correction value for eachcolumn of said array; and storing said each correction value into astorage location of said processor for retrieval by said processor whensaid processor processes image signals from said image sensor in a runmode of operation, (B) the method wherein said finding step includes thestep of discarding a predetermined number of pixels in the column, andidentifying the highest gray scale value present in the remaining pixelsof the column, (C) the method wherein said finding step includes thestep of averaging the pixel values of each pixel in each column, (D) themethod wherein said finding step includes the step of discarding apredetermined number of pixels in a column, and averaging the whitevalues of the remaining pixels, (E) the method wherein in said comparingstep, said predetermined reference value for each column is a constantvalue in the range of column white values for said array, (F) the methodwherein said comparing step includes the step of determining a referencevalue for each column based on an average column white value associatedwit hat least one column surrounding said column for which a referencevalue is currently being determined, and (G) the method wherein saidcomparing step includes the step of determining a reference value foreach column based on an average column white value associated wit hthecolumn for which a reference value is currently being determined and onaverage white values associated with columns surrounding said column forwhich a reference value is currently being determined.

There is described (A) a method for configuring an imaging system in aset-up made of operation so that in a run mode of operation said imagingsystem compensates image signals generated by said imaging system forfixed pattern noise, said imaging system having an image snesorincluding a pixel array and an image processor, said method comprisingthe steps of: exposing said pixel array to a first scene having a firstknown radiance; capturing a predetermined number of image signal framesof said first scene into predetermined storage locations of saidprocessor, said each frame comprising a plurality of pixel values;averaging pixel values of at least one of said pixels to determine afirst average white value for said at least one pixel of said pixelarray when said array is exposed to said first scene; subjecting saidpixel array to a scene having a second known radiance; reading apredetermined number of image signal frames of said second scene intopredetermined storage locations of said processor, said each framecomprising a plurality of pixel values; calculating an average of pixelvalues pertaining to said at least one pixel to determine a secondaverage white value for said at least one pixel of said pixel array whensaid pixel array is exposed said second scene; determining additive termand multiplicative term correction values for said at least one pixelbased on a relationship between said first and second average whitevalues pertaining to said at least one pixel and on said first andsecond scene radiances; and storing said additive term andmultiplicative term correction values into predetermined storagelocations of said processor for retrieval by said processor when saidprocessor processes image signals from said image sensor in a run modeof operation, (B) the method wherein said determining step includes thestep of finding a reference value for said at least one pixel based onthe average white value of at least one neighboring pixel surroundingsaid at least one pixel, (C) the method wherein said determining stepincludes the step of finding a reference value for said at least onepixel based on the average white values of pixels surroundings andincluding said at least one pixel, and (D) the method wherein saidexposing step includes the step of exposing said pixel array to a scenehaving a radiance such that a reading of minimum clipped or maximumclipped pixel value from said array does not result from such exposure.

There is described (A) a method for configuring an imaging system in aset-up made of operation so that in a run mode of operation said imagingsystem compensates image signals generated by said imaging system forfixed pattern noise, said imaging system having an image sensorincluding a pixel array and an image processor, said method comprisingthe steps of: exposing said pixel array to a first scene having a firstknown radiance; capturing a predetermined number of image signal framesof said first scene into predetermined storage locations of saidprocessor and finding a first column white value for each column of saidarray when said each frame is captured, said each frame comprising aplurality of pixel values; averaging column white values of at least oneof said columns to determine a first average column white value for saidat least one column of said pixel array when said pixel array is exposedto said first scene; subjecting said pixel array to a scene having asecond known radiance; reading a predetermined number of image signalframes of said second scene into predetermined storage locations of saidprocessor and identifying a second column white value for each column ofsaid array when said each frame is captured, said each frame comprisinga plurality of pixel values; calculating an average of column whitevalues of at least one of said columns to determine a second averagecolumn white value for said at least one column of said pixel array whensaid pixel array is exposed to said second scene; finding amultiplicative term correction value for said at least one pixel basedon a relationship between said first and secondaverage white valuespertaining to said at least one pixel and on said first and second sceneradiances; determining an additive term correction value for said atleast one pixel based on a relationship between said first and secondaverage white values pertaining to said at least one pixel and on saidfirst and second scene radiances; and storing said multiplicative termand said additive term correction values into predetermined storagelocations of said processor for retrieval by said processor when saidprocessor processes image signals from said image sensor in a run modeof operation, (B) the method wherein said finding step includes the stepof discarding a predetermined number of pixels in the column, andidentifying the highest gray scale value present in the remaining pixelsof the column, (C) the method wherein said finding step includes thestep of averaging the pixel values of each pixel in each column, (D) themethod wherein said finding step includes the step of discarding apredetermined number of pixels in a column, and averaging the whitevalues of the remaining pixels, (E) the method wherein in said comparingstep, said predetermined reference value for each column is a constantvalue in the range of column white values for said array, (F) the methodwherein said comparing step includes the step of determining a referencevalue for each column based on an average column white value associatedwith at least one column surrounding said column for which a referencevalue is currently being determined, and (G) the method wherein saidcomparing step includes the step of determining a reference value foreach column based on an average column white value associated with thecolumn for which a reference value is currently being determined and onaverage column white values associated with columns surrounding saidcolumn for which a reference value is currently being determined.

While the present invention has been explained with reference to anumber of specific embodiments for the purpose of disclosing the bestmode of making and carrying out the invention, it will be understoodthat the spirit and scope of the present invention should be determinedwith reference to the appended claims.

While the present invention has been explained with reference to anumber of specific embodiments for the purpose of disclosing the bestmode of making and carrying out the invention, it will be understoodthat the spirit and scope of the present invention should be determinedwith reference to the appended claims.

1. A method for configuring an imaging system in a setup mode ofoperation so that in a run mode of operation said imaging systemcompensates image signals generated by said imaging system for fixedpattern noise, said imaging system having an image sensor including apixel array and being in communication with a control processor, saidmethod comprising the steps of: exposing said pixel array to a scenehaving a known radiance; capturing a predetermined number of imagesignal frames of said known radiance scene and finding a column whitevalue for each column of said pixel array when said each frame iscaptured, wherein said finding step includes the step of discarding apredetermined number of pixel values in at least one column based ongray scale values of said pixel values; averaging said column whitevalues to determine an average column white value for each column ofsaid pixel array; comparing said each average column white value to apredetermined reference value for each column, and therefrom determininga correction value for each column of said array; and storing said eachcorrection value into a storage location for retrieval by said processorwhen said processor processes image signals from said image sensor insaid run mode of operation.
 2. The method of claim 1, wherein saidfinding step further includes the step of discarding a predeterminednumber of highest gray scale valued pixel values in a column, andidentifying the highest gray scale value present out of the remainingpixel values of the column.
 3. The method of claim 1, wherein saidfinding step includes the step of discarding a predetermined number ofhighest gray scale valued pixel values in a column, and averaging thegray scale values of the remaining pixel values.
 4. The method of claim1, wherein said predetermined reference value of each column is aconstant value in the range of column white values for said array. 5.The method of claim 1, wherein said comparing step includes the step ofdetermining a reference value for each column based on an average columnwhite value associated with at least one column positionally related tosaid column for which a reference value is currently being determined.6. The method of claim 1, wherein said comparing step includes the stepof determining a reference value for each column based on an averagecolumn white value associated with the column for which a referencevalue is currently being determined and on average column white valuesassociated with columns positionally related to said column for which areference value is currently being determined.
 7. The method of claim 1,wherein the method is a method for configuring a monochrome imagingsystem.
 8. The method of claim 1, wherein the method is a method forconfiguring a bar code reading device imaging system.
 9. The method ofclaim 1, wherein said pixel array includes a plurality of rows andplurality of columns of pixels.
 10. A method for configuring an imagingsystem in a setup mode of operation so that in a run mode of operationsaid imaging system compensates image signals generated by said imagingsystem for fixed pattern noise, said imaging system having an imagesensor including a pixel array and being in communication with a controlprocessor, said method comprising the steps of: exposing said pixelarray to a first scene having a first known radiance; capturing apredetermined number of image signal frames of said first scene intopredetermined storage locations of said processor and finding a firstcolumn white value for at least one column of said array when said eachframe is captured, said each frame comprising a plurality of pixelvalues, wherein said finding step includes the step of discarding apredetermined number of pixel values in said at least one column;averaging column white values of at least one of said columns todetermine a first average column white value for said at least onecolumn of said pixel array when said pixel array is exposed to saidfirst scene; subjecting said pixel array to a second scene having asecond known radiance; reading a predetermined number of image signalframes of said second scene into predetermined storage locations of saidprocessor and identifying a second column white value for at least onecolumn of said array when said each frame is captured, said each framecomprising a plurality of pixel values; calculating an average of columnwhite values of at least one of said columns to determine a secondaverage column white value for said at least one column of said pixelarray when said pixel array is exposed to said second scene; determiningadditive term and multiplicative term correction values for said atleast one pixel based on a relationship between said first and secondaverage white values pertaining to said at least one pixel and on saidfirst and second scene radiances; and storing said multiplicative termand said additive term correction values into predetermined storagelocations of said processor for retrieval by said processor when saidprocessor processes image signals from said image sensor in a run modeof operation.
 11. The method of claim 10, wherein said finding stepincludes the step of discarding a predetermined number of highest grayscale valued pixel values in the column, and identifying the highestgray scale value present out of the remaining pixel values of thecolumn.
 12. The method of claim 10, wherein said finding step includesthe step of discarding a predetermined number of highest gray scalevalued pixel values in a column, and averaging the gray scale values ofthe remaining pixel values.
 13. The method of claim 10, wherein themethod is a method for configuring a monochrome imaging system.
 14. Themethod of claim 10, wherein the method is a method for configuring a barcode reading device imaging system.
 15. The method of claim 10, whereinsaid pixel array includes a plurality of rows and a plurality of columnsof pixels.
 16. The method for operating an imaging system so that saidimaging system compensates image signals generated by said imagingsystem for fixed pattern noise, said imaging system having an imagesensor including a pixel array and a control processor, said methodcomprising the steps of: in a setup mode of operation, determining aplurality of correction values corresponding to a plurality of pixels orcolumns of said array; and storing said plurality of correction valuesin a first predetermined memory location of said control processor; in arun mode of operation, capturing a frame of image data comprisinguncorrected pixel values into a second predetermined memory location ofsaid processor; and applying correction values only to selected pixelvalues of said frame when reading said selected pixel values from saidsecond predetermined memory location for further processing, whereinsaid selected pixel values comprise less than all pixel values of saidframe.
 17. The method of claim 16, wherein said method further includesthe step of locating a region of interest comprising a subset of pixelvalues of said frame of image data, and wherein said selected pixelvalues comprise positionally related pixels within said region ofinterest.
 18. The method of claim 16, wherein said selected pixel valuesare corrected for using said correction values when said pixel valuesare read out of said second predetermined memory location for attemptingto decode for any decodable indicia which may be represented in saidcaptured frame of image data.
 19. The method of claim 16, wherein themethod is a method for operating a monochrome imaging system.
 20. Themethod of claim 16, wherein the method is a method for operating a barcode reading device imaging system.
 21. The method of claim 16, whereinsaid pixel array includes a plurality of rows and plurality of columnsof pixels.
 22. A method for configuring an imaging system in a setupmode of operation so that in a run mode of operation said imaging systemcompensates image signals generated by said imaging system for fixedpattern noise, said imaging system having an image sensor including apixel array and being in communication with a control processor, saidmethod comprising the steps of: exposing said pixel array to a scenehaving a known radiance; capturing a predetermined number of imagesignal frames of said known radiance scene and finding a column whitevalue for each column of said array when said each frame is captured;averaging said column white values to determine an average column whitevalue for each column of said pixel array; comparing said each averagecolumn white value to a reference value for each column, and therefromdetermining a correction value for each column of said array, whereinsaid reference value for each column is found by considering averagecolumn white values in columns in positional proximity with said columnfor which said reference value is presently being determinedpreferentially to those columns not in positional proximity with saidcolumn for which said reference value is presently being determined; andstoring said each correction value into a storage location of saidprocessor for retrieval by said processor when said processor processesimage signals from said image sensor in said run mode of operation. 23.The method of claim 22, wherein said comparing step includes the step offinding said reference value for each column based on an average columnwhite value associated with the column for which a reference value iscurrently being determined and on average column white values associatedwith columns positionally related to said column for which a referencevalue is currently being determined.
 24. The method of claim 22, whereinthe method is a method for configuring a monochrome imaging system. 25.The method of claim 22, wherein the method is a method for configuring abar code reading device imaging system.
 26. The method of claim 22,wherein said pixel array includes a plurality of rows and a plurality ofcolumns of pixels.
 27. A method for configuring an imaging system in asetup mode of operation so that in a run mode of operation said imagingsystem compensates image signals generated by said imaging system forfixed pattern noise, said imaging system having an image sensorincluding a pixel array and being in communication with a controlprocessor, said method comprising the steps of: exposing said pixelarray to a scene having a known radiance, said pixel array comprising aplurality of pixels; capturing a predetermined number of image signalframes of said scene into predetermined storage locations of saidprocessor, said each frame comprising a plurality of white values, saideach white value corresponding to one of said pixels; averaging whitevalues corresponding to at least one of said pixels to determine anaverage white value for said at least one pixel of said pixel array;comparing said average white value to a reference value for said atleast one pixel, and therefrom determining a correction value for saidat least one pixel of said array, wherein said reference value is foundby considering average white values of pixels in positional proximitywith said pixel for which said reference value is currently beingdetermined preferentially to those of pixels not in positional proximitywith said pixel for which said reference value is presently beingdetermined; and storing said correction value into a storage location ofsaid processor for retrieval by said processor when said processorprocesses image signals from said image sensor in said run mode ofoperation.
 28. The method of claim 27, wherein said comparing stepincludes the step of finding a reference value for said at least onepixel based on the average white values of a predetermined number ofpixels positionally related to and including said at least one pixel.29. The method of claim 27, wherein the method is a method forconfiguring a monochrome imaging system.
 30. The method of claim 27,wherein the method is a method for configuring a bar code reading deviceimaging system.
 31. The method of claim 27, wherein said pixel arrayincludes a plurality of rows and a plurality of columns of pixels.
 32. Amethod for operating an imaging system, said imaging system having animage sensor including a pixel array and a control processor, saidmethod comprising the steps of: determining a correction value for atleast one pixel or column of said array; and storing said at least onecorrection value in a first predetermined memory location of saidcontrol processor; in a run mode of operation, capturing a frame ofimage data into a second predetermined memory location of saidprocessor; correcting at least one pixel value of said frame using saidcorrection value stored in said first memory location; and launching abar code decoding algorithm for attempting to decode for decodable barcode indicia which may be represented in said frame of image dataincluding said at least one corrected pixel value corrected in saidcorrecting step, wherein said storing step includes the step of storinga column correction value for substantially each column of said pixelarray.
 33. The method of claim 32, wherein said control processorexecutes said correcting step substantially contemporaneously with saidcapturing step, by correcting said at least one pixel value using saidcorrection value while storing said frame of image data into said secondmemory location.
 34. The method of claim 32, wherein said controlprocessor executes said correcting step subsequent to said capturingstep, by storing, in said capturing step, an uncorrected frame of imagedata corresponding to a scene in said second memory location, and byexecuting said correcting step by correcting said at least one pixelvalue using said correction value while reading said uncorrected frameof image data from said second memory location.
 35. The method of claim32, wherein said storing step includes the step of storing a pixelcorrection value for substantially each pixel of said pixel array. 36.The method of claim 32, wherein said storing step includes the step ofstoring a column correction value for substantially each column of saidpixel array.
 37. The method of claim 32, wherein said determining stepcomprises an exposing step including the step of exposing said pixelarray to at least two scenes having different radiances and wherein saidstoring step includes the step of storing a correction value having botha multiplication component and an additive component.
 38. The method ofclaim 32, wherein the method is a method for configuring a monochromeimaging system.
 39. The method of claim 32, wherein the method is amethod for configuring a bar code reading device imaging system.
 40. Themethod of claim 32, wherein said pixel array includes a plurality ofrows and a plurality of columns of pixels.
 41. A method for operating animaging system, said imaging system having an image sensor including apixel array and a control processor, said method comprising the stepsof: determining a correction value for at least one pixel or column ofsaid array; and storing said at least one correction value in a firstpredetermined memory location of said control processor; in a run modeof operation; capturing a frame of image data into a secondpredetermined memory location of said processor; and correcting at leastone pixel value of said frame using said correction value stored in saidfirst memory location; and launching a bar code decoding algorithm forattempting to decode for decodable bar code indicia which may berepresented in said frame of image data including said at least onecorrected pixel value corrected in said correcting step, wherein saiddetermining step comprises an exposing step including the step ofexposing said pixel array to at least two scenes having differentradiances and wherein said storing step includes the step of storing acorrection value having both a multiplication component and an additivecomponent.
 42. The method of claim 41, wherein said control processorexecutes said correcting step substantially contemporaneously with saidcapturing step, by correcting said at least one pixel value using saidcorrection value while storing said frame of image data into said secondmemory location.
 43. The method of claim 41, wherein said controlprocessor executes said correcting step subsequent to said capturingstep, by storing, in said capturing step, an uncorrected frame of imagedata corresponding to a scene in said second memory location, and byexecuting said correcting step by correcting said at least one pixelvalue using said correction value while reading said uncorrected frameof image data from said secondary memory location.
 44. The method ofclaim 41, wherein said storing step includes the step of storing a pixelcorrection value for substantially each pixel of said pixel array. 45.The method of claim 41, wherein said storing step includes the step ofstoring a column correction value for substantially each column of saidpixel array.
 46. The method of claim 41, wherein the method is a methodfor configuring a monochrome imaging system.
 47. The method of claim 41,wherein the method is a method for configuring a bar code reading deviceimaging system.
 48. The method of claim 41, wherein said pixel arrayincludes a plurality of rows and a plurality of columns of pixels. 49.An indicia decoding device configured to correct for fixed patternnoise, said indicia decoding device comprising: an image sensor having aplurality of pixels formed in a two dimensional array of light sensitivepixels, said two dimensional array of light sensitive pixels including aplurality of rows and a plurality of columns of pixels; a controlprocessor processing image data, said control processor being incommunication with said image sensor; a memory unit including a programmemory coupled to said control processor and a working memory coupled tosaid control processor; wherein said indicia decoding device isconfigured to store into said memory unit at least one correctionparameter for correcting a pixel value of a frame of image data, said atleast one correction parameter having a value and being a pixelcorrection value or a column correction value, and wherein said indiciadecoding device has an indicia decoding operating application and isoperable in a run mode of operation; and wherein said indicia decodingdevice when operated in said run mode of operation with said indiciadecoding operating application active (i) stores into said memory unitsaid frame having a plurality of pixel values, (ii) utilizes said atleast one correction parameter to correct at least one pixel value ofsaid frame, and (iii) activates a decoding algorithm for attempting todecode decodable indicia represented in image data including at leastone pixel value corrected utilizing said at least one correctionparameter, wherein said value of said at least one correction parameteris determined prior to a time that said indicia decoding device isoperated in said run mode of operation and wherein said value of said atleast one correction parameter is independent of any image representedin said frame.
 50. The indicia decoding device of claim 49, wherein saidat least one correction parameter is a plurality of correction valuesand wherein said indicia decoding device further when operating in saidrun mode of operation utilizes said plurality of correction values tocorrect for pixel values corresponding to less than all of saidplurality of pixels of said image sensor.
 51. The indicia decodingdevice of claim 49, wherein said indicia decoding device further whenoperating in said run mode of operation avoids reading said at least onecorrection parameter from said memory unit to correct said at least onepixel value until said frame of pixel values is stored into said memoryunit.
 52. The indicia decoding device of claim 49, wherein said indiciadecoding device further has a video display operating application,wherein said indicia decoding device is configured to execute a firstfixed pattern noise correction algorithm when said video displayoperating application is active and a second fixed pattern noisecorrection algorithm when said indicia decoding operating application isactive, the first fixed pattern noise correction algorithm beingdifferent from said second fixed pattern noise correction algorithm. 53.The indicia decoding device of claim 49, wherein said indicia decodingdevice further has a video display operating application, wherein saidindicia decoding device is configured to execute a first algorithm foradjusting pixel values when said video display operating application isactive and a second algorithm for adjusting pixel values when saidindicia decoding operating application is active, the first algorithmbeing different from said second algorithm.
 54. The indicia decodingdevice of claim 49, wherein said indicia decoding device further has avideo display operating application, wherein said indicia decodingdevice is configured to execute a certain fixed pattern noise correctionalgorithm when said video display operating application is active, saidindicia decoding device further being configured to avoid executing saidcertain fixed pattern noise correction algorithm when said indiciadecoding operating application is active.
 55. The indicia decodingdevice of claim 49, wherein said indicia decoding device further has avideo display operating application, wherein said indicia decodingdevice is configured to execute a certain algorithm for adjusting pixelvalues when said video display operating application is active, saidindicia decoding device further being configured to avoid executing saidcertain algorithm for adjusting pixel values when said indicia decodingoperating application is active.
 56. The indicia decoding device ofclaim 49, wherein said indicia decoding device further has a videodisplay operating application, wherein said indicia decoding device isconfigured to correct for a cosine effect when said video displayoperating application is active, wherein said indicia decoding device isfurther configured to avoid correcting for said cosine effect when saiddecoding operating application is active.
 57. The indicia decodingdevice of claim 49, wherein said image sensor is a monochrome imagesensor.
 58. A bar code decoding device, said bar code decoding devicecomprising: an image sensor having a plurality of pixels formed in a twodimensional array of light sensitive pixels, said two dimensional arrayof light sensitive pixels including a plurality of rows and a pluralityof columns of pixels; a control processor processing image data, saidcontrol processor being in communication with said image sensor; amemory unit including a program memory coupled to said control processorand a working memory coupled to said control processor; wherein said barcode decoding device is configured to operate in accordance with a videodisplay operating application and a decoding operating application; andwherein said bar code decoding device is configured to execute a firstfixed pattern noise correction algorithm when said video displayoperating application is active and a second fixed pattern noisecorrection algorithm when said decoding operating application is active,the first fixed pattern noise correction algorithm being different fromsaid second fixed pattern noise correction algorithm.
 59. The bar codedecoding device of claim 58, wherein said first fixed pattern noisecorrection algorithm is an algorithm which corrects for fixed patternnoise attributable to a cosine effect.
 60. The bar code decoding deviceof claim 58, wherein said first fixed pattern noise correction algorithmis a first algorithm which corrects for fixed pattern noise attributableto a cosine effect, and wherein said second fixed pattern noisecorrection algorithm is a second algorithm which does not correct forfixed pattern noise attributable to cosine effect.
 61. A bar codedecoding device, said bar code decoding device comprising: an imagesensor having a plurality of pixels formed in a two dimensional array oflight sensitive pixels, said two dimensional array of light sensitivepixels including a plurality of rows and a plurality of columns ofpixels; a control processor processing image data, said controlprocessor being in communication with said image sensor; a memory unitincluding a program memory coupled to said control processor and aworking memory coupled to said control processor; wherein said bar codedecoding device is configured to operate in accordance with a videodisplay operating application and a decoding operating application; andwherein said bar code decoding device is configured to execute a firstalgorithm for adjusting pixel values when said video display operatingapplication is active and a second algorithm for adjusting pixel valueswhen said decoding operating application is active, the first algorithmbeing different from said second algorithm.
 62. The bar code decodingdevice of claim 61, wherein said first algorithm is an algorithm whichcorrects for fixed pattern noise attributable to a cosine effect. 63.The bar code decoding device of claim 61, wherein said second algorithmis an algorithm which does not correct for fixed pattern noiseattributable to a cosine effect.
 64. The bar code decoding device ofclaim 61, wherein said first algorithm is an algorithm which correctsfor fixed pattern noise.
 65. A bar code decoding device, said bar codedecoding device comprising: an image sensor having a plurality of pixelsformed in a two dimensional array of light sensitive pixels, said twodimensional array of light sensitive pixels including a plurality ofrows and a plurality of columns of pixels; a control processorprocessing image data, said control processor being in communicationwith said image sensor; a memory unit including a program memory coupledto said control processor and a working memory coupled to said controlprocessor; wherein said bar code decoding device is configured tooperate in accordance with a video display operating application and adecoding operating application; and wherein said bar code decodingdevice is configured to execute a certain fixed pattern noise correctionalgorithm when said video display operating application is active, saidbar code decoding device further being configured to avoid executingsaid certain fixed pattern noise correction algorithm when said decodingoperating application is active.
 66. The bar code decoding device ofclaim 65, wherein said certain fixed pattern noise correction algorithmis an algorithm which corrects for fixed pattern noise attributable to acosine effect.
 67. A bar code decoding device, said bar code decodingdevice comprising: an image sensor having a plurality of pixels formedin a two dimensional array of light sensitive pixels, said twodimensional array of light sensitive pixels including a plurality ofrows and a plurality of columns of pixels; a control processorprocessing image data, said control processor being in communicationwith said image sensor; a memory unit including a program memory coupledto said control processor and a working memory coupled to said controlprocessor; wherein said bar code decoding device is configured tooperate in accordance with a video display operating application and adecoding operating application; and wherein said bar code decodingdevice is configured to execute a certain algorithm for adjusting pixelvalues when said video display operating application is active, said barcode decoding device further being configured to avoid executing saidcertain algorithm for adjusting pixel values when said decodingoperating application is active.
 68. The bar code decoding device ofclaim 67, wherein said certain algorithm is an algorithm which correctsfor fixed pattern noise attributable to a cosine effect.
 69. The barcode decoding device of claim 67, wherein said image sensor is amonochrome image sensor.
 70. The bar code decoding device of claim 67,wherein said bar code decoding device is configured to adjust pixelvalues when said decoding operating application is active.
 71. The barcode decoding device of claim 67, wherein said certain algorithm is analgorithm which corrects for fixed pattern noise.
 72. A bar codedecoding device, said bar code decoding device comprising: an imagesensor having a plurality of pixels formed in a two dimensional array oflight sensitive pixels, said two dimensional array of light sensitivepixels including a plurality of rows and a plurality of columns ofpixels; a control processor processing image data, said controlprocessor being in communication with said image sensor; a memory unitincluding a program memory coupled to said control processor and aworking memory coupled to said control processor; wherein said bar codedecoding device is configured to operate in accordance with a videodisplay operating application and a decoding operating application; andwherein said bar code decoding device is configured to execute a certainalgorithm for adjusting pixel values when said decoding operatingapplication is active, said bar code decoding device further beingconfigured to avoid executing said certain algorithm for adjusting pixelvalues when said video display operating application is active.
 73. Thebar code decoding device of claim 72, wherein said bar code decodingdevice is configured to adjust pixel values when said video displayoperating application is active.